Lens protein undergoes a number of age related changes: (1) there is a formation of polypeptides which have greater and smaller molecular weights than those found in young lenses; (2) the protein has a tendency to form larger aggregates; and (3) there is a formation of a protein associated yellow color and an unusual fluorescence. The cummulative effect of these changes is an opacification of the lens, or cataract. The objective of this research is to define the photochemical effect of near UV irradiation on human lens protein at the molecular level and correlate them with those seen on the macromolecular level. Experiments will and have been performed to isolate and to compare compounds produced photochemically in vitro with those found in human cataractous lenses. In addition to protein, the lens also contains a number of low molecular weight constituents (photosensitizers, quenchers, etc.) which may influence the course of any photochemical reaction. Their effect, if any, will be assessed at the molecular level. These experiments will attempt to show the extent to which the age related changes in human lens protein are due to photochemical reactions.